Electrical apparatus



Sept. 24,1946. D. A. BELL El 'AL 2,403,192

- ELECTRICAL APPARATUS Filed Aug. 11, 1942 2 Sheets-Sheet l W m if v.

Sept. 24, 1946.

ELECTRICAL APPARATUS Filed Aug. 11, 1942 2' Sheets-Sheet 2 D. A. BELL ETAL ,408,192

Patented Sept. 24, 1946 v David ArthurBell and Arthur Henry 'Ashford- Wynn, London,. England, assignors'to A. -C.

' Cossor Limited, London of Great Britain England, a company Application August ll, 1942, Serial No."454,391

In Great Britain August 16, 1941 7 Claims. 1

This-invention relates to the thermionic valve feedback oscillator of the kind in which the frequency' is controlled by a reactance valve. A reactance valve is a thermionic valve, having a control grid excited substantially in phase quadrature with the generated oscillatory voltage, and so connected that its output current ofoscillation frequency flows through at least part of the tuned circuit which substantially determines'the frequency of the oscillator. In this manner there is introduced into the tuned circuit an effective reactance, the magnitude of which is dependent upon the mutual conductance of thereactance valve. The phase quadrature voltage for the control grid is usually obtained from the generated oscillatory voltage by means 'of a phase-shifting network-comprising a resistance in series with a reactance, r I 7 Oneof the difficulties in' arranging a circuit of this kind'for operation at'very high'frequencies is the amount of power dissipated in the resistance of the phase-shifting network At such frequencies the reactance is very low, even if it consists simply of inter-elec'trodeand' stray ca- 'pacities; and the resistance-must therefore also be low in order that sufficient voltage may be developed across the reactance. 'An object-of the present invention is to overcome this difficulty. The invention is applied to oscillators wherein the tuned circuit which substantially determines the frequency of the oscillator is of the parallelresonant type, and -wherein'the output'current of oscillation frequency of the oscillator valve flows through at least part of said tuned'circuit. In an oscillator in which the invention' is carried into effect the substantially phase'quadrature voltage for the reactance valve control "grid is developed across a reactance which is effectively connected in series between the tuned cir-' cuit and the oscillator valveso that it carries the oscillation frequency output current'of the oscillator valve.

It is desirable that the oscillator valve should have high impedance, so that the inclusion .of the reactance in series shall not seriously disturb the phase relationship of the anode current and the anode'voltage.v 1 In, a preferred arrangement, the reactance across which the control grid vol a flfor the reactance v'alve is developed is efiectively connected between the tuned circuit and the cathode of the'os'cillator valve, and either one end or the other of this reactance is maintained at earth or other zero oscillation potential.

In an oscillator in which a: modified formiof theinvention is carried into effect in amanner which is preferable for some purposes, the reactance across which the control grid voltage for the reactance valve is developed is arranged to carry, not only the oscillation frequency. output current of the oscillator valve, but also the oscillation frequency output current of the reactance valve. This'arra'ngement will somewhat disturb the phase relationships, and will lessen the degree of frequency control obtainable for a given change in mutual conductance of the reactance valve; but these disadvantages may sometimes be unimportant, especially if only a small degree of frequency control is required.

Intheaccompanying drawings each of the figures shows the circuit diagram of an oscillator embodying the invention.

1 Figure l, showsan oscillator ge erally similar to the Hartley oscillator.

Figure 2 shows an oscillator generally similar to the Colpittsoscillator. I

Figures 3 and 5 show oscillators eachgenerally similar to the ordinary tuned-anode oscillator.

Figure .4 shows an oscillator generally similar to' the ordinary cathode-coupled oscillator.

In Figure 1, for the oscillator valve V1, a pentode is selectedyto provide the necessary high impedance. Its suppressor grid is directly connected to cathode, while, its screen grid is maintained. at constant positive potential relative to cathode by condenser C15 and resistance R13, the latter connected to the positive high tension line. The direct current supply from the high tension line to the anode is provided through resistance R11. g

The oscillation frequency output current of valve V1 passes from its anode through blocking condenser C1zto the tuned circuit L101, which substantially determines the oscillation frequency; and thence from the tapping on inductance L1 (which'tapping in the Hartley oscillator is normally connected directly to cathode) .to cathode'throughthe capacitancesci and Cs, effectively in parallel with each other, through condenser C5 designedtooffer negligible reactance 'at the oscillating frequency. In parallel with capacitance C4, choke Ch is provided to carry the direct component of the anode'current of reactancevalve V2. -Capacitance C4 may consist solely of the stray capacity across choke Ch and capacitance C9 may consist solely of the interelect-rode andstray capacities between control gridandcathode of valve V2 .Thevcontrol grid of valve ,V1'is coupled to the lower end of tunedcircuit L101 by condenser C3,

directly connected to cathode, while its screen grid is maintained at constant positive potential relative to cathode by condenser Cs and'resistance R3, the la ter connected to the positive high tension line. The direct current supply from the;- high tension line to the anode of valve-V2 ,iprm V vided through resistance R1.

The control grid of valve Vziscoupleda-to earth for oscillation frequencies by condenserCs'} and,v

the voltage developed across capacitances C fand C9, in parallel with each other, is applied between control grid and cathode of valve V2: This voltage will be in quadrature with the oscillation-free quency output current of oscillator valve V1, which flows through these capacitances. Theoscillation frequency output current of reactance valve V2 will; therefore; be in quadrature with that: of oscillator -valveVn It path is from the anode of 'valve' V2, through blocking condenser C7,. to the'sa-me endof tuned oircuitlirCi thatisi'coupled through condenser C12'to the anodeof valve V1. From the tapping on inductance L1itis returned directly to' cathode of valve-V2. It will,.therefore; introduce into the-tunediicircuit L101 an'effective reactance,- the magnitude of which is dependent up on the mutual conductance' offreactance valve V2;

The mutual conductance of "valve- V2 iscontrolled by direct current source B'.in series 'zwith modulating source -E.' The oscillation frequency coupling condenser-C5 should-offer high reactance at modulation frequencies.

Figure 2 shows a circuit=diagram of an oscillator embodying the invention, but 1 generally similar to the Colpitts oscillator; The oscillation frequency output current of "valve Vi passesrfrom i it's anode through blocking condenser'fliz tothe tuned circuit L1C1C21 From the tapping-oncomdenser' chain C1'C2 (which tapping in the Colpitts oscillatoris normally connected 'dire'ctly to cathode), it passesthroughcapacitance CQ'and osciL lation frequency coupling condenser C's-to: the earthed cathode of valveVi'; The capacitance C9 may consist solelyof interrelectrode and stra; capacities between control grid'and cathodeof valve V2. Condenser C5, as inFi'gure 1, offers negligible reactance-at oscillation frequencies but high reactance at modulationifrequencies;

The oscillation frequency output current of reactance valve V2 passes from its anode through blocking condenser C7 to the tuned circmtL1C1C2. From thetapping on condenser chain C102 it passes/through capacitance C5 to the'cathodeof valve V2 The'capacitance Ct, across which :the control grid; voltage for valveVz is developed, therefore carries the oscillation frequency output currents of both of-valves V1 andVz. The'quadrature relationship between the oscillation fre quency output currents of the twovalves will therefore be somewhat disturbedL Figure 3' shows the circuit diagramof an 0scillator embodying the invention but generally similar to the ordinary tuned-anode'oscillator. Capacitances Cl and C9 are effectively connected iiiparallel with each other for oscillation frequencies, and in series between theearthedend of tuned'cifcuitL'rCi andthe cathode of valve V1; the oscillation frequency-output" current of valve V1 therefore-flows through'these capacitances. Choke Ch carries theD. Ci'component of the anode current of oscillator valve V1 and also maintains the mean potential of the control grid of valve V2.

The control grid voltage for valve V1 is provided by coil L2 coupled with inductance L1 of the tuned circuit L1C1.

The oscillation frequency control) grid voltage for--valve V1i-is developed across capacitances C4 and C9 in parallel with each other. The oscillation frequency output current of valve V2 passes 1. throughblocking condenser C1 to the tuned circuit' L1C1' to earth, and thence through oscillation-vlfrequencycoupling condenser C5 to the cathodeiofzvalveVz.

FigureA shows the circuit diagram of an oscillator'embodying the invention but generally similar to the ordinary cathode-coupled oscillator;v The oscillation frequency output current of valve V1 flows from anode through the high tension source (which may be provided with a by-pass condenser not shown) to earth and thencetothe tuned .icircuit. L101. From .thetappingr on; inductance: L1 it: passes-. to. cathode through-capacitances C4 and Cain parallel" with each; other (condenser; C5 offering negligible 1 reactance at oscillation frequencies) The direct component-.ofitheaanode current of valve V1 is passed: from cathode to earth throughj choke Ch andrthelower part of inductance L1.

The oscillation frequencwoutputi current. oi valve V2 ipassesthrough blocking condensenCr to ther:tuned circuit L101. From thertapping on inductance L1 it is returned; directly to the f cathode of: valve V2. Thepmutual conductance: of reactance" valve= V2 is controlled by direct. current source B inaseries with modulation source E, connected betweenearth and control grid; Choke cm; which offers, lowreactance, at modulation frequencies but high reactance at oscillation frequencies; is inserted; to prevent; shortt-circuiting of; the; control grid :of '1valver:V2- to earth,- for: oscillationfrequency:v Condenser C5 cifersrhighreactance, and-choke Chi low reactance; .atmodulationfrequenciea so the cathodes of both valves are at zero; potential forqmod-ulation' frequencies.

Figure :5 shows the circuit. diagram' of :another oscillatorzembodying the invention but-generally similar toitheaordinarytuned anode. oscillator. Unlike. that shown-in, Figure 3, this circuit isarrangedso-that'the cathodes of the. two valves are directly" connected"' together; Capacitances C4 and; C1 areagain effectively Y connected inparallel: with each other "for: oscillation frequencies, al'idxin: series betweenthe cathode ofvalve V1 and. the-earthed end of" tunedcircuit; L1C1; condenser G5- offering negligible reactance at'. oscillation frequency.

The oscillation frequency output current of valve V2 passes through'blocking condenser Cw to the tuned circuit: L'1C1 and thence through capacitances Grand C9 in-parallelfwith each other t'Oithe' cathode-oft valve V2. As in Figure 2, therefore, the capacitances C4 and C13, in parallel-witheach other, carry the oscillation frequency output currents of both of'valves- V1 and V2.

To obtain a high degree of frequency control for a given modulating voltage, it is desirable to apply the modulating voltage to the control grid oil the reactance valve. This arrangement has been. indicated, ineeach of the. circuit diagrams shown inthedrawings-t Themutualconductance of valve V2 :ma-y, however, alternatively I be. conf trolled by modulating; the. potential of the screen grid, or of the suppressor. grid; Qfjthereactance valve, while maintaining these grids always at cathode potential for oscillation frequencies.

The invention may be applied for the purpose of obtaining a frequency modulated signal, and themodulating source may then be for example a source of speech currents or of television signals. The invention may alternatively be applied for the purpose of automatic frequency control and the modulating source will then be a frequency error detector.

We claim:

1. In a system for generating oscillations of controllable frequency, an electron discharge tube having oscillation generating electrodes and a parallel-tuned oscillation circuit operatively coupled to said electrodes to produce sustained electrical oscillations of a frequency-determined by the resonant frequency of said circuit, reactive impedance means exterior of and connected in series between an electrode of said tube and said circuit so as to be traversed by substantially the total oscillation current to said circuit and to develop an oscillation potential relatively phase shifted with respect to the generated oscillation potential, a reactance control electron tube having input and output circuits coupled to said reactive impedance means and said oscillation circuit, respectively, and means for varying the out-' put oscillation current of said reactance tube to correspondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

2. In a system for generating oscillations of controllable frequency, an electron discharge tube having oscillation generating electrodes and a parallel-tuned oscillation circuit operatively coupled to said electrodes to produce sustained electrical oscillations of a frequency determined by the resonant frequency of said circuit, reactive impedance means exterior of and connected in series between an electrode of said tube and said circuit so as to be traversed by substantially the total oscillation current to said circuit and to develop an oscillation potential relatively phase shifted with respect to the generated oscillation potential, a reactance control electron tube having at least a cathode, a grid and an anode, means for coupling the grid-cathode path of said reactance tube to said reactive impedance means and for coupling the anode-cathode path of said reactance tube to said oscillation circuit, and further means for varying the output oscillation current of said reactance tube to correspondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

3. In a system for generating oscillations of controllable frequency, an electron discharge tube having oscillation generating electrodes and a parallel-tuned oscillation circuit operatively coupled to said electrodes to produce sustained electrical oscillations of a frequency determined by the resonant frequency of said circuit, capacitative reactance means exterior of and connected in series between an electrode of said tube and said circuit so as to be traversed by substantially the total oscillation current to said circuit and to develop an oscillation potentialrelatively phase shifted with respect to the generated oscillation potential, a reactance control electron tube having input and output circuits coupled to said reactance means and said oscillation circuit, re-

' spectively, and means for varying the output oscillation current of said reactance tube to cor- 6 respondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

4. In a system for generating oscillations of controllable frequency, an electron discharge tube having oscillation generating electrodes and a parallel-tuned oscillation circuit operatively coupled to said electrodes to produce sustained electrical oscillations of a frequency determined by the resonant frequency of said circuit, inductive reactance means exterior of and connected in series between an electrode of said tube and said circuit so as to be traversed by substantially the total oscillation current to said circuit and to develop an oscillation potential relatively phase shifted with respect to the generated oscillation potential, a reactance control electron tube having input and output circuits coupled to said reactance means and said oscillation circuit, respectively, and means for varying the output oscillation current of said reactance tube to correspondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

5. In a system for generating oscillations of controllable frequency, an oscillator comprising an electron discharge tube having oscillation generating electrodes and a resonant oscillation generating circuit determinative of the generated frequency and operatively connected to said electrodes to maintain sustained electrical oscillations,

I said circuit being traversed by the oscillation output current of said tube, reactance means connected in series between an electrode of said tube and said oscillation circuit, a reactance control electron tube having input and output circuits coupled to said reactance means and to said oscillation circuit, respectively. and means for varying the output oscillation current of said reactance tube to correspondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

6. In a system for generating oscillations of controllable frequency, an oscillator comprising an electron discharge tube having a cathode and an anode, a resonant oscillation generating circuit determinative of the generated frequency and connected to said anode and cathode, and means to maintain sustained oscillation in said circuit, reactive impedance means connected in series between said oscillation circuit and said cathode, a reactance control electron tube having input and output circuits coupled with said impedance means and said oscillation circuit, respectively, and means for varying the oscillation output current of said reactance tube to correspondingly V vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

'7. In asystem for generating oscillations of controllable frequency, an electron discharge tube having oscillation generating electrodes and an oscillation circuit operatively coupled to said electrodes to produce sustained electrical oscillameans and having an output circuit connected to both said oscillation circuit and said reactance means to cause said reactance means to be traversed by'the oscillation frequency output current of both said oscillator tube and said reactance tube, and means for varying the output oscillation current of said reactance tube to cor- '8 respondingly vary the effective resonant frequency of said oscillation circuit and to thereby control the frequency of the oscillations produced.

DAVID ARTHUR BELL. ARTHUR HENRY ASHFORD WYNN. 

